JPH07104157B2 - Distance detector for camera - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device that projects light onto a subject and detects the distance to the subject based on the light receiving position of reflected light from this.

(Prior Art) For distance detection in a camera, a light emitting element and a light receiving element are arranged at a constant interval, light from the light emitting element is projected onto a subject, and the reflected light is received by a light receiving element as a light spot,
A so-called active distance measuring device is used which measures the distance to a subject based on the position of a light spot by the principle of triangulation.

Such active distance detecting devices are roughly classified into two types according to the light emitting form of the light emitting element. The first is to continuously light up the light emitting element while modulating the light emitting element at a constant frequency, for example, several tens KHz. Has a one-shot method in which a single flash is emitted for each ranging operation.

In the former method, only the signal component tuned to the modulation frequency of the light emitting element is selectively taken out by the bandpass filter to reduce the influence of external light as much as possible and improve the reliability of the distance measurement data. However, since it requires a capacitor and a reactance coil that form a bandpass filter, there is a problem that the number of external parts increases and the number of times becomes large, making it difficult to incorporate the camera.

On the other hand, according to the latter method, since the light emitting element can be operated by the instantaneous rating to emit strong light, the range can be expanded, and the bandpass filter is not required, and the circuit configuration is simplified and the size is small. On the other hand, the ability to discriminate between the light from the light emitting element and the light from the lighting equipment that is in a blinking state, such as a fluorescent lamp, a neon sign, a strobe device, etc., is low. There is a problem that a large error may be included.

(Object) The present invention has been made in view of such a problem, and an object of the present invention is to provide a camera distance capable of obtaining highly reliable distance measurement information while taking advantage of the single-shot light emission method. It is to provide a detection device.

(Summary of the Invention) That is, a feature of the present invention is that a light emitting element and a light receiving element are arranged at a certain distance, and the light emitting element is caused to emit light in response to a signal from a microcomputer to illuminate a subject. In a distance detection device in which reflected light from a subject is converted into an electric signal by a light receiving element as the position of spot light related to the distance to the subject, the light emitting element is caused to emit light at least a plurality of times during a distance measurement period. The point is that the distance signal for each light emitting operation is converted into the number of steps, and the one having the higher frequency of the number of steps is used as the distance increase.

(Examples) Therefore, the details of the present invention will be described below based on illustrated examples.

FIG. 1 shows an outline of the present invention, in which a light emitting element 1 and a light receiving element 2 are arranged at a fixed distance L, and a light emitting element circuit 4 which operates by a signal from a microcomputer 3 is shown.
The light-emitting element 1 is caused to emit light in a single shot in accordance with the signal of 1., and this light is applied to the subject S through the condenser lens 5, while the reflected light from the subject S is converted into spot light by the condenser lens 6 and received. The position of the spot light received by the element 2 and related to the distance to the subject is converted into an electric signal, this signal is converted into a pulse width signal by the distance measuring circuit 7 and input to the microcomputer 3, and the pulse motor M takes an image. It is configured to drive the distance adjusting mechanism of the lens A.

FIG. 2 shows the details of the above-mentioned device, in which reference numeral 1 is a condenser lens 5 in the optical axis direction of the taking lens.
It is a light-emitting element that emits light via a transistor, and when a high-level signal is output from the microcomputer 3, the transistor is turned on.
A predetermined time interval, for example, every 10 milliseconds is predetermined by a signal from the light emitting element drive circuit 4 configured to output the electric charge charged in the capacitor 43 to the light emitting element 1 when 41 and 42 become conductive. In addition, the light is emitted a plurality of times, for example, about eight times.

Reference numeral 2 denotes a spot light position detector that receives light from the optical axis direction of the taking lens at the focal position of the condenser lens 6, and has a cathode terminal 2a and two anode terminals 2b and 2c, and corresponds to the spot light position. It is configured to output current signals I ₁ and I ₂ .

Reference numerals 71 and 72 are head amplifiers for receiving the signals of the spot light position detector 2, respectively. The current signals from the anode terminals 2b and 2c of the spot light position detector 2 are converted into voltages by the amplifiers 71a and 72a. Capacitors 71c, 72c via 72b
Is charged to control the transistors 71d and 72d, and the light emitting element 1
Signal lower than the frequency component of the pulsed signal due to
That is, it is configured to bypass the signal caused by the external light and thereby improve the dynamic range for the pulsed signal.

A logarithmic conversion circuit 73 is a sum (I ₁ + I ₂ ) of an operational amplifier 73a that logarithmically compresses the current signal I ₁ from _one head amplifier 71 and current signals I ₁ and I ₂ from the head amplifiers 71 and 72. It is composed of an operational amplifier circuit 73b for logarithmically compressing and a differential amplifier circuit 73c for calculating the difference between the signals logI ₁ and log (I ₁ + I ₂ ) from the operational amplifier circuits 73a, 73b, which are proportional to the distance to the subject. To a logarithmic expander 75 composed of a diode via a voltage follower 74 which is configured to output a current signal logI ₁ / (I ₁ + I ₂ ) and which operates in response to a data hold signal output from the microcomputer. It outputs the current signal I ₁ / (I ₁ + I ₂ ) proportional to the distance to the double integrator circuit 76 described later.

Reference numeral 76 denotes the double integration circuit described above, which includes an operational amplifier 76a and a capacitor 76b having a capacity capable of holding a current signal for each time, and receives a current signal via the switch S1 which is turned on by the data hold signal described above. Further, the current source 77 is supplied with a current via a switch S2 which is turned on by a read signal from the microcomputer 3.

Reference numeral 78 is a pulse width conversion circuit, which has an initial potential depending on the read signal.
The pulse width is converted to a pulse width proportional to the time required to charge the capacitor 76 of the double integration circuit 76 up to V _0, and the pulse width is output to the microcomputer 3 via the AND gate 79.

Reference numeral 3 in the figure represents the above-mentioned microcomputer,
Upon receiving a signal input from the switch B which is linked to the release button of the camera, a series of operations is executed based on a flow chart described later, and the distance measuring operation control unit 31 that controls the entire distance measuring operation and the distance measuring circuit 7 A / D converter 3 that converts a pulse representing a distance signal from the signal into a digital signal based on a clock
2 and an arithmetic processing unit 33 that converts the digital signal into the number of steps and controls the pulse motor.
Since the arithmetic processing unit 33 converts the digital data temporarily stored in the memory means 33a, that is, the number of clocks into the number of steps, as shown in FIG. 3, the number of clocks within a certain range, C _{0 to} C ₁ , C _{1 to} C ₂ ...... C _{6 to} C ₇ as addresses, and a step number conversion means 33b as a dictionary having step numbers S ₀ , S ₂ ...... S ₇ as data, and the frequency of the number of steps from now on. Therefore, the frequency counting means is provided with a step number counting counter as shown in FIG.

Next, the operation of the apparatus thus configured will be described based on the timing chart shown in FIG. 5 and the flowchart shown in FIG.

When the power of the camera is turned on to perform the distance measurement, the voltage due to the external light incident on the spot light position detector 2 is charged in the capacitors 71c and 72c, and the voltage is matched with the external light via the transistors 71d and 72d. The current is bypassed to ground and the integrating capacitor 76b connects to the current source 77 via switch S2.
It is charged to the initial potential V ₀ by receiving the current supplied from.

In this state, when the camera is aimed at the subject and the release button is operated to turn on the distance measurement switch B, the first distance emission signal is output from the distance measurement operation control unit 31, and the light emission element drive circuit 4 emits light. The element 1 is caused to emit light to illuminate the subject. This light is reflected by the subject, converted into spot light by the condenser lens 6, and enters the spot light position detector 2. As a result, the spot light position detector 2 outputs a current correlated with the position of the spot light from each of the terminals 2b and 2c. Since this current signal is smaller than the time constants of the head amplifiers 71 and 72, it passes through this and becomes a distance signal logarithmically compressed by the logarithmic conversion circuit 73. The distance measurement operation control unit 31 outputs a data hold signal when a certain time ΔT ₁ has elapsed from the start of light emission, that is, when the distance signal becomes stable, and outputs the logarithmic signal to the logarithmic expansion circuit 75 via the voltage follower 74. It is output and converted into a current signal, and is input to the integration circuit 76 for a fixed time ΔT ₂ via the switch S1. As a result, the potential of the integrating capacitor 76b drops by ΔV ₁ from the initial potential V ₀ .

When the first light emission ends, the light emitting element 14 cuts off the supply of the drive current and naturally cools to prepare for the next light emission. At the same time, the distance measurement operation control circuit unit 31 outputs the read signal to turn on the switch S2.
Then, the capacitor 76b is charged with a constant current from the current source 77. Since this charging time Δt ₁ is proportional to the amount of electric charge ΔV ₁ accumulated in the capacitor 76b, the pulse width Δt ₁ becomes the distance signal.

The pulse signal is converted into a digital signal by the analog-digital conversion section 32, converted into a step number by the step number conversion means 33b, and output to the frequency counting means.

When the set pause time ΔT ₃ has elapsed, the integrating capacitor 76b is supplied with the current from the current source 77 via the switch S2 and returns to the initial potential V ₀ . Distance measurement control unit 31
Outputs the second light emission signal to cause the light emitting element 1 to emit light and irradiate the same subject with light. As a result, a current signal corresponding to the distance from the light spot position detector 2 to the object is output, and this current signal is converted into a distance signal by the logarithmic conversion circuit 73, and then logarithmically expanded by the data hold signal before switching. It is input to the capacitor 76b for a fixed time ΔT ₂ via S _1, and the potential of the capacitor 76b is reduced by the potential difference ΔV ₂ matching the distance signal, converted into a digital signal, and then output to the frequency counting means 33c. In the process of converting to this number of steps, those that belong to a certain range of clocks are counted as the same number of steps, so the number of steps is practically accurate regardless of the error caused by the distance measuring circuit etc. Will be calculated.

Thereafter, the light emitting element 1 is distanced a predetermined number of times with the interval ΔT ₃ in this manner to obtain the number of steps, which is stored in the frequency counting means 33c.

When the predetermined distance measurement operation is completed, the work distance operation control means 31
Reads out the maximum number of steps from the frequency counting means 33c as distance information and outputs it to the pulse motor M which drives the distance adjusting mechanism.

As a result, the number of steps due to a distance measurement error that occurs during a series of distance measurement operations is excluded, and highly reliable distance information can be obtained.

In the above-described embodiment, the number of steps with the largest number of times is output as distance information after the specified number of distance measuring operations are completed. However, as shown in FIG. When the number of steps is sequentially stored in the means, when one step reaches a predetermined number of times, for example, three times, the distance information of the number of steps is output and the subsequent distance measuring operation is stopped. As a result, the number of times of distance measurement can be reduced as much as possible under conditions where the distance measurement environment is favorable, and highly reliable distance information can be obtained when the distance measurement environment is poor.

(Effect) As described above, according to the present invention, the light emitting element is caused to emit light at least a plurality of times during the distance measurement period, the distance signal for each light emitting operation is converted into the number of steps, and the frequency of the number of steps is high. Since this is used as the distance information, even if a distance measurement error occurs, this data is excluded, and while utilizing the advantages of the single light emission method, highly reliable distance information can be obtained. Since the frequency is detected after conversion into the number of steps, the frequency counting can be simplified with sufficient accuracy in imaging.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of the present invention, FIG. 2 is a circuit diagram showing the details of the same device, and FIGS. 3 and 4 are schematic diagrams showing one embodiment of a step number converting means and a frequency counting means, Fifth,
FIG. 6 is a waveform diagram and a flow chart showing the operation of the same apparatus, respectively, and FIG. 7 is a flow chart showing another embodiment of the present invention. 1 ... Light emitting element 2 ... Optical spot position detecting element 3 ... Microcomputer 7 ... Distance measuring circuit 71, 72 ... Head amplifier 73 ... Logarithmic conversion circuit 74 ... Voltage follower 75 ... Logarithmic expansion circuit 76 ... … Double integration circuit 76b… Integration capacitor 78… Pulse width conversion circuit S1, S2… Switch A …… Shooting lens M …… Pulse motor

Claims (1)

[Claims] 1. A light-emitting element and a light-receiving element are arranged at a fixed distance, and the light-emitting element is caused to emit light by a signal from a microcomputer to irradiate the subject, while the reflected light from the subject reaches the subject. In a distance detection device configured to convert an electric signal by a light receiving element as a position of a spot light related to a distance, the light emitting element is caused to emit light at least once a plurality of times during a distance measurement period, and a distance for each light emitting operation. A distance detecting device for a camera, wherein a signal is converted into the number of steps, and information having a high frequency of the number of steps is used as distance information.